Long term evolution (LTE, Long Term Evolution) is a standard being studied and refined currently by the 3rd generation partnership project (3GPP, 3rd Generation Partnership Project). In an LTE wireless communication system, to support technologies such as dynamic scheduling and downlink multiple input multiple output (MIMO, Multiple Input Multiple Output) transmission, a terminal needs to report channel state information (CSI, Channel State Information) to a base station through a physical uplink control channel (PUCCH, Physical Uplink Control Channel) and a physical uplink shared channel (PUSCH, Physical Uplink Shared Channel), where the CSI includes channel quality information (CQI, Channel Quality Information), precoding matrix indicator (PMI, Precoding Matrix Information) and rank indication (RI, Rank Indication).
In dynamic scheduling, the terminal is notified of scheduling information related to each scheduling time point through physical downlink control channel (PDCCH, Physical Downlink Control Channel) signaling, which provides great flexibility but also causes a heavy signaling load. For a regular low-rate service, such signaling overheads are especially significant. To reduce the signaling load of such service, the 3GPP defines a manner of semi-persistent scheduling (SPS, Semi-Persistent Scheduling), and the idea is that for the regular low-rate service, resources are allocated on a long-time basis and it is unnecessary to send PDCCH signaling to perform dynamic scheduling at each time of transmission. Usually, an SPS service is activated and deactivated by PDCCH signaling, where activating PDCCH signaling carries scheduling information such as resource allocation. Before the service is deactivated, the terminal sends new data packets at fixed periods according to the related scheduling information which is allocated when the service is activated, unless there is new PDCCH signaling to update the related scheduling information during the periods.
In an LTE R8 system, main MIMO transmission modes include single antenna port transmission, transmit diversity, and spatial multiplexing. In closed loop spatial multiplexing mode, a terminal needs to be notified of corresponding precoding information, that is, a precoding matrix indicator (PMI, Precoding Matrix Indicator), where the PMI is normally carried by PDCCH allocation information (grant). The MIMO transmission mode of the terminal is usually configured by a base station semi-statically. In the LTE R8 system, even if the transmission mode configured by the base station for a PDSCH is spatial multiplexing, a downlink SPS service of a terminal only supports transmit diversity for the following three reasons: One is that, a PDCCH grant is provided when the SPS service is activated, but subsequent data transmission has no corresponding PDCCH grant, and therefore, the PMI required for spatial multiplexing is unavailable; the second is that a data packet corresponding to the SPS service is small and does not need to be transmitted in two streams; the third is that transmit diversity also provides good transmission performance. In the LTE R8 system, the PUSCH only supports the single antenna port transmission mode, and therefore, the uplink SPS only supports the single antenna port transmission mode.
According to the latest progress of the 3GPP standard, in LTE R10, the closed loop spatial multiplexing technology will be used in the uplink while the transmit diversity technology will not be adopted. Then, if the MIMO transmission mode configured by the base station for the PUSCH is spatial multiplexing, while in an existing SPS mechanism, no PDCCH grant is provided except for the initial transmission so that the PMI is unavailable, and the single antenna port transmission mode has to be returned to.